diff --git a/ChangeLog b/ChangeLog
index 4ed25a3091..680489b568 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Dec 19 19:34:03 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* object.c (rb_mod_const_get): nul byte is invalid as constant name.
+
 Wed Dec 19 17:54:18 2012  Masaya Tarui  <tarui@ruby-lang.org>
 
 	* vm_trace.c (rb_threadptr_exec_event_hooks): get rid of race
diff --git a/object.c b/object.c
index b4e67bab5b..b05b41be25 100644
--- a/object.c
+++ b/object.c
@@ -1920,7 +1920,7 @@ rb_mod_const_get(int argc, VALUE *argv, VALUE mod)
 {
     VALUE name, recur;
     rb_encoding *enc;
-    const char *pbeg, *p, *path;
+    const char *pbeg, *p, *path, *pend;
     ID id;
 
     if (argc == 1) {
@@ -1946,6 +1946,7 @@ rb_mod_const_get(int argc, VALUE *argv, VALUE mod)
     }
 
     pbeg = p = path;
+    pend = path + RSTRING_LEN(name);
 
     if (!*p) {
 	rb_raise(rb_eNameError, "wrong constant name %s", path);
@@ -1957,10 +1958,10 @@ rb_mod_const_get(int argc, VALUE *argv, VALUE mod)
 	pbeg = p;
     }
 
-    while (*p) {
+    while (p < pend) {
 	VALUE part;
 
-	while (*p && *p != ':') p++;
+	while (p < pend && *p != ':') p++;
 
 	if (pbeg == p) {
 	    rb_raise(rb_eNameError, "wrong constant name %s", path);
diff --git a/test/ruby/test_module.rb b/test/ruby/test_module.rb
index b2e2e8049d..eb1477893b 100644
--- a/test/ruby/test_module.rb
+++ b/test/ruby/test_module.rb
@@ -582,10 +582,19 @@ class TestModule < Test::Unit::TestCase
   end
 
   def test_const_get_invalid_name
+    c1 = Class.new
+    assert_raise(NameError) { c1.const_get(:foo) }
+    bug5084 = '[ruby-dev:44200]'
+    assert_raise(TypeError, bug5084) { c1.const_get(1) }
+    assert_raise(NameError) { Object.const_get("String\0") }
+  end
+
+  def test_const_defined_invalid_name
     c1 = Class.new
     assert_raise(NameError) { c1.const_defined?(:foo) }
     bug5084 = '[ruby-dev:44200]'
     assert_raise(TypeError, bug5084) { c1.const_defined?(1) }
+    assert_raise(NameError) { Object.const_defined?("String\0") }
   end
 
   def test_const_get_no_inherited